1. Field of the Invention
The present invention relates to a data communication system, such as a facsimile system, capable of multi-polling communication between a polling transmitter and a polling receiver.
2. Related Background Art
Multi-polling communication is presently proposed by ITU-T, and an example of the protocol therefor is shown in FIG. 12. As shown in FIG. 12, a DIS signal contains a signal (ms bit) indicating the presence or absence of the multi-selection function, and, if the signal is xe2x80x9c1xe2x80x9d indicating the presence of the multi-selection function, a polling-receiver sets the ms bit of a DTC signal at xe2x80x9c1xe2x80x9d when it requests the multi-polling.
On the other hand, a polling-transmitter transmits an EOS (end-of-selection) signal after the transmission of a document, and the polling-receiver transmits a DTC signal in case of requesting a next document or a MCF signal in case of not requesting the next document.
In the above-explained configuration, however, in case of conducting the next polling reception, the polling-receiver is incapable of informing the polling-transmitter that the document has been correctly received. Also, training operations cannot be effectively selected since RTN and RTP signals cannot be transmitted.
After the transmission of the EOS signal, the polling-transmitter also receives SEP/DTC signal, which is not defined in the conventional T-30 protocol. Therefore, a trouble may be generated in the communication.
In consideration of the foregoing, an object of the present invention is to provide a data communication system capable of effectively executing the multi-polling communication.